This proposal is to study mechanisms of immunological injury to vascular endothelium and to develop an assay for pulmonary endothelial injury. Human angiotensin converting enzyme, which is a constituent of the luminal membrane of endothelium, will be purified. The purified enzyme will be used to develop an enzyme-linked immunoassay to detect circulating antibodies in patients with systemic lupus erythematosus, progressive systemic sclerosis and adult respiratory distress syndrome. Polyclonal and monoclonal antibodies to angiotensin converting enzyme will be produced. These will be tested for their interaction with membrane bound enzyme in human endothelial cell culture. Platelet activating factor release and coagulant activity will be measured. Monoclonal antibodies will be tested for their specificity for pulmonary angiotensin converting enzyme. A specific monoclonal antibody will be used to assay for circulating pulmonary enzyme released during endothelial injury.